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Predicting Adverse Perinatal Outcomes in Gestational Diabetes

Is a single fasting glucose measurement sufficient to predict risk of adverse perinatal outcomes?

According to the ADA, gestational diabetes mellitus (GDM) is diagnosed in the second or third trimester and not clearly associated with type 1 or type 2 diabetes. Screening for GDM is recommended at 24-48 weeks in women who were not previously diagnosed. GDM treatment is meant for glycemic control which in turn reduces the risks of large baby syndrome, childhood complications, and obesity.

OGTT is the first-line test for diagnosis of GDM, but it has many shortcomings among them being the fact that it cannot be duplicated, it is very time-consuming, and it is stressful for both the pregnant women and the test administrator. These shortcomings lead to introduction of uncertainty of OGTT in predicting big baby syndrome. In the past, studies suggested that fasting plasma glucose tests were more reliable to predict large gestational age when compared to postprandial glucose levels irrespective of the mothers’ body mass index and the 2-hour glucose level. This finding was confirmed by a recent systematic review by Farrar et al done in 2016. According to the ADA, GDM can be diagnosed using either the one-step strategy or the two-step strategy. Using the one-step strategy, diagnosis is confirmed when any the following are present: FPG is ≥92mg/dL, 1-hr glucose level is ≥180mg/dL and 2-hr glucose level is ≥153 mg/dL. Using the two-step strategy, diagnosis is confirmed when at least two of the following are present: Fasting plasma glucose ≥95 mg/dL or ≥105 mg/dL, 1-hr plasma glucose ≥180 mg/dL or ≥190 mg/dL, 2-hr plasma glucose ≥155 mg/dL or ≥165 mg/dL and 3-hr ≥140 mg/dL or ≥145 mg/dL. This clearly shows that uncertainty still exists regarding whether a single FPG measurement is enough to predict increased risk of adverse perinatal outcomes.

In the Born in Guangzhou Cohort Study (BIGCS), 15,198 pregnant women were recruited in the study between February 2012 and June 2012 and the association between maternal glucose perinatal outcomes evaluated. Of these, 12,594 were evaluated for LGA with a prevalence of 1,325. Association was found to be strongest for LGA among categorical outcomes at 95% CI; (1.17-1.37). Fasting glucose, birth weight, birth weight Z score, and LGA had a stronger relationship compared to 1-hr and 2-hr OGTT glucose levels. AUC of FPG for LGA was higher than 1-hr OGTT (0.611 vs. 0.566, P < 0.0001) and 2-hr OGTT (0.611 vs. 0.551, P < 0.0001) glucose level. Caesarian section and spontaneous preterm outcomes also had smaller AUCs than LGA.

In conclusion, glucose levels were directly proportional to the LGA with FBG having the strongest relationship compared to 1-hr glucose and 2-hr glucose. Therefore, both the 1-hr and 2-hr OGTT glucose levels had a lower influence on LGA prediction compared to FPG. A single FPG screen can therefore be a sufficient and valid parameter to determine the level of risk of LGA in Chinese population. Use of a single parameter of FPG to determine risk of LGA would reduce the stress associated with the multiple tests that are performed currently and save costs for both the patient and the hospital. The results of this study are generalizable, but distribution at 1-hr and at 2-hr should be re-evaluated in other populations.

Practice Pearls:

  • Fasting glucose had a stronger direct relationship with large-for-gestational age than postprandial glucoses.
  • Single fasting glucose has comparable predictive ability of large for gestational age to 75g OGTT.
  • Single fasting glucose level is a sufficient alternative for identifying increased risk of large for gestational age

References:

Xia h. Mol WJ. Qiu X. et al. Single Fasting Plasma Glucose Versus 75-g Oral Glucose-Tolerance Test in Prediction of Adverse Perinatal Outcomes: A Cohort Study. EBioMedicine February 2017 Volume 16, Pages 284–291. DOI: http://dx.doi.org/10.1016/j.ebiom.2017.01.025

Josephat Macharia, PharmD candidate, Lecom School of Pharmacy class of 2018